Random copolymers (RCPs), such as propylene-based RCPs, are useful in applications where good optical properties and/or lower meting temperature for sealing performance are required. As comonomer content increases (e.g., ethylene content) in RCPs, they will become sticky at a certain point. The point at which they become sticky may vary with temperature and catalyst system. For example, Ziegler-Natta catalyzed RCPs with 6-7 wt % or higher ethylene or certain metallocene (MCN) catalyzed RCPs with 2-3 wt % or higher (i.e., 3-4 mol % or higher) ethylene have not generally been produced in slurry or gas phase reactors at desired temperatures (e.g., 50-80° C.) due to stickiness and reactor fouling problems. See Resconi, L., Fritze, C., “Metallocene Catalysts for Propylene Polymerization,” Pasquini N (ed), Polypropylene Handbook, 2nd Edition, Hanser Publisher, Munich (2005), 117 and 13. The melting temperature difference between Ziegler-Natta derived RCPs and MCN derived RCPs is thought to be a major cause of the different ethylene incorporation limits.
Given these issues, polymers such as RCPs having an ethylene content above a certain point generally must be produced in solution phase polymerization processes utilizing a solvent at temperatures above 120° C., and typically above 135° C. The reactor effluent in these processes is a liquid solution comprising the polymer and a substantial amount of solvent. To obtain the final product, the solvent must be separated from the polymer. To do this, the reactor effluent is typically heated under pressure in a separator to create a solvent-rich phase and a polymer-rich phase, and then both phases are subject to further separation by bifractionation. The process is time-consuming and not cost effective.
It would be more efficient and economical to be able to make these polymers using a supported catalyst system in gas or slurry phase. Gas phase processes do not require substantial use of solvents or the corresponding sophisticated separation processes. In these processes, the reactor is typically a fluidized bed comprising monomer and comonomer primarily in the gas phase and fluidized solid particles comprising catalyst components and polymer. The reactor effluent comprises solid polymer granules, rather than a liquid solution of polymer in solvent. Slurry processes, on the other hand, still use substantial amounts of solvents but usually involve much simpler processes for separating solvent from the product than solution phase processes.
Both gas and slurry processes, however, have conventionally been limited in their ability to make certain MCN catalyzed RCPs with higher than 2-3 wt % ethylene incorporation at preferred temperatures of 50-80° C. without reactor fouling. Some semi-crystalline rubbers have been produced in gas or slurry processes, but these processes require the addition of an anti-sticking agent such as carbon black to the reactor to reduce the possibility of fouling and assist in polymer handling. As such, the processes are extremely messy and often require dedicated equipment to prevent contamination. It would be advantageous to be able make these polymers in gas or slurry phase without the requirement of anti-sticking agents. It would also be advantageous to be able make RCPs with high enough comonomer content to obtain the desired Tm for heat seal properties, while maintaining the ability of the polymer to stay in granular form and be free-flowing at desired gas or slurry phase process conditions.
Recently, efforts have also been made to take advantage of newly developed MCN catalyst technology to capitalize on the benefits such catalysts provide. Polymers prepared with such single-site catalysts often have narrow molecular weight and composition distributions, low extractables, and a variety of other favorable properties. Recent efforts have also focused on new support structures for single-site catalysts, and the use of different supports to affect polymer properties. Highly porous supports, such as high surface area silicas, have been used in polymerization processes. However, such supports have not generally been used in gas or slurry phase polymerization processes for making certain MCN catalyzed RCPs with comonomer content higher than 2-3 wt %.
Background references on the use of high surface area silicas include WO 2004/092225, which discloses MCN polymerization catalysts supported on silica having a 10-50 μm particle size (PS), 200-800 m2/g surface area (SA), and 0.9 to 2.1 mL/g pore volume (PV), and shows an example of a 97 μm PS, 643 m2/g SA and 3.2 mL/g PV silica (p. 12, Table I, support E (MS3060)) used to obtain isotactic polypropylene (pp. 18-19, Tables V and VI, run 21).
EP 1 380 598 discloses certain MCN catalysts supported on silica having a 2-12 μm PS, 600-850 m2/g SA, and 0.1 to 0.8 mL/g PV, and shows an example of silica having a 6.9 μm PS, 779 m2/g SA and 0.23 mL/g PV (p. 25, Table 3, Ex. 16) to obtain polyethylene.
EP 1 541 598 discloses certain MCN catalysts supported on silica having a 2 to 20 μm PS, 350-850 m2/g SA, and 0.1 to 0.8 mL/g PV (p. 4, lines 15-35), and shows an example of a 10.5 μm PS, 648 m2/g SA and 0.51 mL/g PV silica (see p. 17, Example 12) for an ethylene polymerization.
EP 1 205 493 describes a 1126 m2/g SA and 0.8 cc/g structural porous volume (small pores only) silica support used with an MCN catalyst for ethylene copolymerization (Examples 1, 6, and 7).
JP 2003-073414 describes a 1 to 200 μm PS, 500 m2/g or more SA, and 0.2 to 4.0 mL/g PV silica, but shows examples of propylene polymerization with certain MCNs where the silica has a PS of 12 μm and 20 μm.
JP 2012-214709 describes 1.0 to 4.0 μm PS, 260 to 1000 m2/g SA, and 0.5 to 1.4 mL/g PV silica used to polymerize propylene.
Other references of interest include US 2011/0034649; US 2011/0081817; Madri Smit et al., Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 43, pp. 2734-2748 (2005); and “Microspherical Silica Supports with High Pore Volume for Metallocene Catalysts,” Ron Shinamoto and Thomas J. Pullukat, presented at “Metallocenes” Europe '97 Dusseldorf, Germany, Apr. 8-9, 1997.
There is need for new catalyst systems, supports, and processes that enable polymers like propylene-based RCPs with low melting temperatures (e.g., less than or equal to 140° C. or less than or equal to 135° C.) or ethylene-based copolymers with low melting temperatures (e.g., less than or equal to 110° C., 105° C., or 100° C.) to be produced in gas and slurry phase processes without the use of substantial amounts of solvents and/or anti-sticking agents. There is a need for processes that take advantage of the favorable properties that highly porous supports and single-site and MCN catalysis technology can provide to produce polymers that meet the needs of particular applications, such as providing one or more of: improved economics by making polymers in low cost in use processes, improved toughness or other properties, low extractables, bimodal MWD, bimodal composition distribution, bimodal PS distribution (PSD), and combinations thereof. There is a need for gas and slurry phase processes that enable the production of polymers such as propylene-based RCPs in a single reactor.